The Beaded Lizard or Mexican Beaded Lizard, Heloderma horridum, is a venomous lizard found in Mexico and the southern United States. Adult Mexican Beaded Lizards range from 13 to 18 inches in length. Until recently, the beaded lizard and the Gila Monster were the only two lizards known to be venomous. Research showed that some iguanas and monitors are also venomous. The beaded lizards' venom is similar to that of some snakes (e.g. the western diamondback rattler).